The invention relates to an oxidation furnace for the oxidative treatment of fibres, in particular for the production of carbon fibres, having                a) a housing which, apart from passage regions for the fibres, is gas-tight;        b) a process chamber situated in the interior of the housing;        c) an atmosphere device by means of which a hot working atmosphere can be generated and blown into the process chamber;        d) deflecting rollers which are arranged outside the process chamber in deflecting regions and guide the fibres side by side in the form of a fibre carpet through the process chamber in a serpentine manner, wherein the fibre carpet spans a plane between opposing deflecting rollers.        
In such oxidation furnaces, the deflecting regions are typically sited outside the furnace housing in order on the one hand to permit intervention on the fibre and on the other hand to prevent inadequate aeration upon deflection at the process temperature. By arranging the deflecting rollers outside the furnace, the fibre is guided at the process temperature out of the process chamber through a lock region in the direction towards the deflecting roller. In the lock region, the fibre is cooled in order to stop the oxidation reaction, the temperature in the lock region being so chosen that gaseous substances from the atmosphere are prevented from condensing out. When the fibre leaves the furnace, the fibre accordingly at least has the temperature prevailing in the lock region. At least some of this heat energy is dissipated to the surrounding atmosphere on the path to the deflecting roller, during deflection and on the path back towards the furnace, or in the case of contact with the deflecting roller to the deflecting roller itself. The fibre accordingly passes through the lock again into the furnace with a significantly lower temperature and must be heated to the process temperature again. The energy loss thus caused by cooling is considerable. It is accordingly constructive to prevent the thread from cooling or deliberately to induce cooling in such a manner that the energy that is released can be fed back to the system again.
During operation of an oxidation furnace, work must be carried out in particular in the deflecting regions and at the deflecting rollers. For example, the fibre carpet may have to be straightened at a deflecting roller if fibres run off track. Individual fibres can also tear as they pass through the oxidation furnace. The loose end of a torn fibre is conventionally linked in the region of the deflecting rollers to an adjacent fibre, which then carries the torn fibre through the oxidation furnace. When carrying out such activities it is consequently beneficial to achieve low temperatures of the fibres in the deflecting region and further to keep the ambient temperature in the region of the deflections low, that is to say only slightly above ambient temperature.